A luminescent lyotropic liquid-crystalline gel of a water-soluble Ir(III) complex

Article abstract of DOI:10.1016/j.molliq.2021.116187

In the present study, the synthesis and properties of a novel water soluble Ir(III) complex of formula [(ppy)₂Ir(dpq)]CH₃CO₂ is described, where ppy is the cyclometalated 2-phenylpyridine ligand and dpq the dipyrido[3,2-f:2′,3′-h]quinoxaline used as ancillary ligand. Own to its specific molecular structure, this complex forms highly ordered supramolecular gels in water on a wide range of concentration, from 3 to 14% w/w. The gel phase shows birefringence under cross polarisers that is completely loss when water is removed, evidence of the formation of a true lyotropic liquid-crystalline gel, without the need of an additional gelator. The gel is macroscopically formed of entangled microfibers that can be seen under optical microscope and that display luminescent properties as observed by confocal microscopy. X-Ray diffraction allowed to resolve the structure of the lyotropic mesophase that is formed by columns of complex cations organised in a tetrahedral manner which are in turn arranged in a larger oblique lattice, hence showing a high degree of order. The photophysical properties of the complex in its different state of matter (solid, gel phase and xerogel) are presented and discussed.

Full text of DOI:10.1016/j.molliq.2021.116187

Journal of Molecular Liquids 334 (2021) 116187
Contents lists available at ScienceDirect
Journal of Molecular Liquids
journal homepage: www.elsevier.com/locate/molliq
A luminescent lyotropic liquid-crystalline gel of a water-soluble Ir(III)
complex
Francesca Scarpelli a, Loredana Ricciardi b, Massimo La Deda a,b, Elvira Brunelli c, Alessandra Crispini a,
Mauro Ghedini a, Nicolas Godbert a, , Iolinda Aiello a,b
⇑
a MAT-INLAB (Laboratorio di Materiali Molecolari Inorganici), LASCAMM CR-INSTM, Unità INSTM della Calabria, Dipartimento di Chimica e Tecnologie Chimiche, Università
della Calabria, 87036, Arcavacata di Rende, CS, Italy
b Consiglio Nazionale delle Ricerche, Istituto di Nanotecnologia - Nanotec, UOS di Cosenza, Ponte Pietro Bucci Cubo 31/C, 87036 Rende, CS, Italy
c Dipartimento di Biologia, Ecologia e Scienze della Terra, DIBEST, Università della Calabria, 87036, Arcavacata di Rende, CS, Italy
a r t i c l e i n f o
a b s t r a c t
Article history:
In the present study, the synthesis and properties of a novel water soluble Ir(III) complex of formula
[(ppy)2Ir(dpq)]CH3CO2 is described, where ppy is the cyclometalated 2-phenylpyridine ligand and dpq
the dipyrido[3,2-f:20,30-h]quinoxaline used as ancillary ligand. Own to its specific molecular structure,
this complex forms highly ordered supramolecular gels in water on a wide range of concentration, from
3 to 14% w/w. The gel phase shows birefringence under cross polarisers that is completely loss when
water is removed, evidence of the formation of a true lyotropic liquid-crystalline gel, without the need
of an additional gelator. The gel is macroscopically formed of entangled microfibers that can be seen
under optical microscope and that display luminescent properties as observed by confocal microscopy.
X-Ray diffraction allowed to resolve the structure of the lyotropic mesophase that is formed by columns
of complex cations organised in a tetrahedral manner which are in turn arranged in a larger oblique lat-
tice, hence showing a high degree of order. The photophysical properties of the complex in its different
state of matter (solid, gel phase and xerogel) are presented and discussed.
Received 20 January 2021
Revised 26 March 2021
Accepted 14 April 2021
Available online 17 April 2021
Keywords:
Metallogels
Lyotropic liquid-crystalline gels
Luminescence
Ó 2021 Elsevier B.V. All rights reserved.
1. Introduction
whatever their chemical nature, are able to generate in specific sol-
vents a typical tangled network of fibers within a solid-like phase
Recently, a new promising class of soft materials, named lyotro-
pic liquid-crystalline gels (LLCGs), has been investigated [1]. LLCGs
are multicomponent soft materials consisting of at least a gelator
and a lyotropic liquid crystal (LLC) in a solvent or solvents mixture
[2-6]. In order to prepare LLCGs, surfactant molecules, such as
sodium dodecyl sulphate (SDS) [4], potassium laurate (KL) [3] or
dimyristoyl phosphatidyl choline (DMPC) [7], are generally used
as LLCs. These molecules are characterized by a polar head and a
hydrophobic tail and, being LLCs, present a mesophase in a specific
solvent [8]. For these LLCs, gelation can be induced by either using
a low-molecular-weight gelator [4] or a polymer [3,9-11]. Exam-
ples of low-molecular-weight gelators used to gelate LLCs include
[12,14-16]. Therefore, LLCGs have been developed to increase the
mechanical stability of LLCs [17], but also to provide gels with
specific optical properties [2] or a precise alignment [13]. These
hybrid materials combine indeed the long-range orientational
order of mesophases with the mechanical properties and the
fibrous network of a gel phase [1,3,4]. LLCGs are appealing materi-
als since they might find applications as sensors and actuators,
thanks to their stimuli-responsive nature, as well as displaying
interesting features for their potential use in biomedical applica-
tions [1]. For example, Al-Zahrani et al. developed a controlled
delivery system loading metronidazole in a LLCG consisting of a
surfactant mixtures (Span 80 – Tween 80), PVA and sesame oil
[9]. Furthermore, although electrochemical applications have not
yet been explored for LLCGs, the development of electrochemical
and electrooptical devices based on liquid-crystalline physical gels,
the thermotropic counterpart of LLCGs, have been reported [18].
Thus, through the appropriate choice of their components, one
might expect LLCGs to be useful materials for this application field
as well [1].
12-hydroxyoctadodecanoic
acid
(12-HOA)
[4],
1,3:2,4-
dibenzylidene-D-sorbitol (DBS) [5] and tris-amido-cyclohexane
derivatives (HG) [12], whereas polyacrylamide (PAAm) [3], poly-
ethylene glycol diacrylate (PEG-DA) [13] or polyvinyl alcohol
(PVA) [9] can act as polymeric gelators. All these gelator molecules,
⇑
Corresponding author.
E-mail address: nicolas.godbert@unical.it (N. Godbert).
https://doi.org/10.1016/j.molliq.2021.116187
0167-7322/Ó 2021 Elsevier B.V. All rights reserved.

F. Scarpelli, L. Ricciardi, M. La Deda et al.
Journal of Molecular Liquids 334 (2021) 116187
Besides these classical examples of LLCGs, several molecules
with both gelating and mesogenic properties have been reported
[19-28]. In particular, Bowman et al. recently demonstrated that
the phosphatidylcholine moiety combined with thymine and a tri-
azole ring (TTPC, Chart 1d), in water and in a specific range of con-
centrations, acts simultaneously as gelator and as lyotropic
mesogen [27], differently from DMPC, in which the phosphatidyl-
choline portion behaves exclusively as mesogen [7]. Moreover,
Kuang et al. described a series of amino-acid-based dendrons able
to gelate benzyl alcohol and, at the same time, to generate lyotro-
pic mesophases in the same solvent [23,24]. In addition, a room
temperature ionic liquid, 1-decyl-3-methylimidazolium bromide,
forming a lyotropic liquid crystalline gel in water, has been
depicted by Firestone et al. [25] In this case, the dried sample dis-
plays orientational disorder, but the addition of a suitable amount
of water induces the creation of an anisotropic arrangement of
CO2. The ligand dpq has been already incorporated in Ir (III) com-
plexes, but for biological purpose, since its lipophilicity and
intercalating ability can promote the biological membranes perme-
ation and the interaction with DNA, respectively [42,43]. In addi-
tion to its high tendency to generate
p-p interactions, it is worth
to note that dpq, with flat four fused ring, is the nitrogen analogue
of triphenylene, the molecular fragment usually representing the
core of discotic liquid crystals, which generate columnar assem-
blies [41,44,45]. Furthermore, the presence of two nitrogen atoms
within the structure of dpq could promote the instauration of
hydrogen bonds with surrounding water molecules hence increas-
ing the overall solubility of the resulting [(ppy)2Ir(dpq)]CH3CO2
complex in water. For the same reasons, we also expected a greater
self-assembling ability with respect to the analogous previously
reported compounds, which could in turn generate more organized
supramolecular structures. In this regard, increasing the aromatic-
molecules within
a
free-flowing gel phase. All the above-
ity by using dppz was expected to reinforce the p-p interactions
mentioned systems can be considered as one-component LLCGs,
thus fluids preserving the orientational order of a crystalline solid,
which do not flow in the steady-state. To best of our knowledge,
only one example of organometallic compound, a dinuclear chro-
mium (II) complex [Cr2(L-tart2H)(phen)2]Na, with both gelating
and mesogenic properties in water, has been reported [29]. The
lyomesophase has been hypothesised to have a chiral lamellar
structure consisting of monolayers of molecules, formed by exten-
sive stackings between the phen groups and separated by layers of
water. It is worth to note that, although this Cr(II) compound does
not belong either to the conventional lyotropic class (amphiphilic
molecules) or to that of chromonic LCs, it generates a real lyotropic
mesophase, also characterized by very high viscosity and by the
presence of ribbon-like aggregates [30,31]. Note that chemical
structures of all the above mentioned examples can be viewed in
supporting information (Chart S1).
within the supramolecular edifice, leading to a further improve-
ment. Herein, we describe the synthesis and the supramolecular
organization of the [(ppy)2Ir(dpq)]CH3CO2 complex in water,
investigated through microscope analysis, Powder X-Ray Diffrac-
tion (PXRD) and Differential Scanning Calorimetry (DSC). Further-
more, the photophysical features of this compound in its
different state of matter (solid, gel phase and xerogel) have been
examined.
2. Results and discussion
2.1. Synthesis and self-assembling properties in water
The cationic water-soluble Ir(III) complex [(ppy)2Ir(dpq)]CH3-
CO2 (1) was synthetized starting from the cyclometalated Ir(III)
chloro-bridged dimer [(ppy)2Ir(l-Cl)]2 (I). Following previous
Several supramolecular Ir (III) assemblies, including gels, liquid
crystals, soft salts, coordination polymers and metal–organic
frameworks (MOFs), have been described [32]; however, to date,
no Ir (III) complexes generating true lyotropic liquid crystalline
gel phases have been reported. Recently, various luminescent
hydrogels based on discrete cationic Ir (III) complexes, incorporat-
ing 2-phenylpyridine H(ppy) as cyclometalated ligand, bipyridine
(bpy) or 1,10-phenantroline (phen) as ancillary ligands and hydro-
philic counterions, have been reported (Chart 1) [33-35]. However,
the supramolecular organization of these Ir(III) hydrogels is clearly
visible only in the corresponding air dried gels (xerogels), as it gen-
erally happens in true gel phases [35-41]. On this basis, considering
these highly organized hydrogels generated by Ir (III) complexes,
we evaluated the possibility of increasing the gel order almost up
to liquid-crystalline organization, in order to obtain a lyotropic
liquid-crystalline gel comprising only one chemical species. Hence,
more aromatic and extended ligands, dipyrido[3,2-f:20,30-h]qui
noxaline (dpq) and dipyridophenazine (dppz) were selected as
ancillary ligand, in place of bpy, for the synthesis of analogous Ir
(III) compounds, [(ppy)2Ir(dpq)]CH3CO2 and [(ppy)2Ir(dppz)]CH3-
reports on the use of microwave (MW) irradiation to promote
cycloplatination [46] and cycloiridation [33,47,48], this dimeric
precursor was obtained by MW-assisted synthesis in degassed
(N2) 2-ethoxyethanol/water solution at 250 W, using Ir(III) chloride
as metal source and 2-phenylpyridine, H(ppy), as cyclometalated
ligand. The synthetic procedure adopted to prepare Ir(III) complex
1, involved two steps: first, a bridge-splitting reaction was per-
formed by the addition of the ancillary ligand dipyrido[3,2-f:20,30-
h]quinoxaline (dpq) to the precursor (I), obtaining the correspond-
ing intermediate complex [(ppy)2Ir(dpq)]Cl (IIa), then an anion-
exchange with silver acetate (CH3COOAg) allowed the formation
of the desired [(ppy)2Ir(dpq)]CH3CO2 (1) complex. Through an
identical pathway and by using as ancillary ligand dipyri-
dophenazine (dppz) instead of dpq, compound [(ppy)2Ir(dppz)]
CH3CO2 (2) was also obtained (Scheme 1).
The first indication that both complexes 1 and 2 display inter-
esting interactions with water molecules is observable through
their 1H NMR in deuterated chloroform (see ESI for all 1H NMR
spectra). Indeed, the chemical shift of the water residual peak of
2.1 ppm (for 1) and 2.3 ppm (for 2) clearly appears at lower
Chart 1. Highly ordered reported Ir(III) hydrogels [33,34].
2

F. Scarpelli, L. Ricciardi, M. La Deda et al.
Journal of Molecular Liquids 334 (2021) 116187
Scheme 1. Reagents and reaction conditions: (i) IrCl3ꢁnH2O, EtOCH2CH2OH/H2O, 250 W, 110 °C, 1 h; (ii) dpq or dppz, MeOH/CH2Cl2, N2, reflux, 24 h; (iii) CH3COOAg, MeOH,
4 h.
magnetic field with respect to their corresponding chloride precur-
sors, 1.6 ppm (for IIa) and 1.7 ppm (for IIb). This evidence strongly
suggests the institution of hydrogen bonding interactions between
the acetate anions and the water molecules.
microscope (Fig. 1a). Up to now, only few examples of supramolec-
ular aggregates, large enough to be detected with an optical micro-
scope, have been reported [51-53]. Indeed, generally, in order to
analyze the morphology of supramolecular assemblies, electron
microscopy is required. The presence of elongated structures indi-
cates that directional intermolecular interactions drive the self-
assembly of the Ir (III) compound. The superstructures observed
for the 3%-10% w/w gel phases of [(ppy)2Ir(dpq)]CH3CO2 appear
as a tangle of wires and exhibit birefringence, thus an anisotropic
arrangement of the molecular building blocks can be reasonably
assumed within the fibres (Fig. 1c and d). Furthermore, these bire-
fringent fibres acquire great mobility and start to flow upon heat-
ing (Fig. 1e), until the isotropy temperature (Ti) is reached. Ti
depends on the sample concentration and at this temperature,
both birefringence and all fiber aggregates disappear. Lastly, a sub-
sequent cooling of the specimen leads to the reappearance of the
birefringent fibres, which self-organize in structures resembling
braided hair (Fig. 1f).
The fibres still persist after dehydration of these samples (3–
10% w/w), thus in the corresponding xerogels, although birefrin-
gence is completely loss in this solid state. The presence of a
fibrous network, as already mentioned, is usually ascribed to gels.
A deep insight of the fibre-shaped superstructures was provided
by Transmission Electron Microscopy (TEM) analysis of a gel sam-
ple that was left to dry at room temperature prior to analysis. TEM
micrographs clearly show the presence of the supramolecular
wires even in the dried sample (Fig. 2a). Moreover, every macro-
fiber is actually composed by a variable number of smaller wires
which twist around themselves, as it is possible to observe under
higher magnification (Fig. 2b).
Compound 1, similarly to the parent complexes [(ppy)2Ir(bpy)]
CH3CO2,[49] [(ppy)2Ir(phen)]CH3CO2 [34] and [(ppy)2Ir(bpy)]X
(X = EtOꢀ, OH–, EtOCH2COꢀ2 , MeOCH2COꢀ2 ) [33,35], shows the abil-
ity to gelate water, generating a viscous phase. However, this com-
plex creates gel-phases in water in a range of concentration much
larger than the above-mentioned compounds, which is from 3% to
14% w/w, the latest corresponding to the solubility limit of the
complex in water. The larger range of concentration for water gela-
tion with respect to the Ir (III) parent compounds can be ascribed
to the more efficient self-assembling ability of the dpq ligand. On
the other hand, extending further the aromaticity of the ancillary
ligand drastically decreases the overall solubility of the Ir(III)
cation in water. Indeed compound 2 with a dppz ligand is nearly
insoluble in water, preventing any further study on its supramolec-
ular organization properties. The gel-phases of 1 were prepared by
dissolving the opportune quantity of complex in warm distilled
water. The clear solutions, obtained upon heating the mixtures in
a closed tube, were slowly cooled down to room temperature.
The formation of gel phases, thus the absence of flow in the
steady-state, was determined through a typical inversion test tube
experiment [50]. Noteworthy, the solution-gel transition is com-
pletely reversible, since the gel-phase turns into solution either
upon heating or shaking (sonication) and this cycle can be repeated
indefinitely, evidence of the non-covalent nature of the interac-
tions established between the molecular building blocks, and the
high tendency of this complex to self-assemble in water.
The gel phases of [(ppy)2Ir(dpq)]CH3CO2 (1) exhibit intense and
homogeneous birefringent textures under POM (Fig. 3a), as
reported for the analogous complexes [(ppy)2Ir(bpy)]CH3CO2
[49], [(ppy)2Ir(phen)]CH3CO2 [34] and [(ppy)2Ir(bpy)]X (X = EtOꢀ,
OH–, EtOCH2CO2ꢀ, MeOCH2COꢀ2 ) [33,35]. The most concentrated gel
phase (14% w/w) was selected as example and its POM micro-
graphs are reported in Fig. 3. In these most concentrated samples,
the supramolecular fibres are no longer visible at room tempera-
ture. This could be explained considering that in these highly vis-
cous specimens the superstructures are too close and packed
together to be clearly distinguished. However, the presence of
3. Microscopy studies
The water gel phases of compound 1 at different concentrations
were observed under a Polarizing Optical Microscope (POM). The
samples were placed in closed cells in order to avoid evaporation
of the solvent, hence preventing any change of the gel concentra-
tion during observation. Surprisingly, the supramolecular phases
at concentrations within the range of 3%–10% w/w present elon-
gated fibres, already visible through the 10x objective of an optical
3

F. Scarpelli, L. Ricciardi, M. La Deda et al.
Journal of Molecular Liquids 334 (2021) 116187
Fig. 1. POM micrographs of the gel phases originated by [(ppy)2Ir(dpq)]CH3CO2 in water: (a) 3% w/w, r.t., 10x Microscope Objective (MO); (b) 3% w/w, r.t., 50x MO; (c) 3%w/
w, r.t., 20x MO; (d) 6% w/w, r.t., 20x MO; (e) 4% w/w, 37 °C, 20x MO; (f) 4% w/w, 28 °C, 20x MO. Images c, d, e and f were acquired between two crossed polarizators.
Fig. 2. TEM images of the dried sample of a gel phase of [(ppy)2Ir(dpq)]CH3CO2 (a-scale bar 5 lm; b-scale bar 2 lm).
these supramolecular wires was confirmed by their appearance
upon heating (Fig. 3b). Indeed, the birefringent texture of the
14% w/w gel phase disappears at ca. T = 49 °C and, during the tex-
ture vanishing, the birefringent fibres become well visible and per-
sist in the sample up to the temperature of 50 °C, after which they
fade. Upon cooling, at ca. 40 °C the re-assembly of the wires is
noticeable (Fig. 3c). Further decrease in temperature leads to a
new ring-banded spherulites texture that emerges at 33 °C
(Fig. 3d) and becomes gradually more defined (Figs. 3e and f). Such
a defined texture, typical of liquid-crystalline materials [54], has
4

F. Scarpelli, L. Ricciardi, M. La Deda et al.
Journal of Molecular Liquids 334 (2021) 116187
First heating-cooling cycle
Second heating-cooling cycle
Fig. 3. POM micrographs of the 14% w/w gel phases originated by [(ppy)2Ir(dpq)]CH3CO2 in water: (a) r.t; (b) first heating, 49 °C; (c) first cooling, 40 °C; (d) first cooling, 33 °C
(e) first cooling, 32 °C; (f) magnification of (e); (g) second cooling, 40 °C; (h) and (i) second cooling, 40 °C, with and without crossed polarizers, respectively; (j) second cooling,
33 °C; (k) second cooling, 32 °C; (l) second cooling, r.t.
not been observed in the previously reported analogous Ir (III)
complexes. In addition, a second heating-cooling cycle was per-
formed in order to better investigate the anisotropic arrangement
of molecules in these samples. During the second heating cycle,
the same trend experienced during the first cycle was observed,
thus at ca. 49 °C the texture dissolving occurred, followed by the
disappearance at ca. 50 °C of the wires. However, in the course of
the second cooling, at first the birefringent fibers appear (Fig. 3g)
which gradually enlarge themselves (Fig. 3h) and which are evi-
dent also without crossed polarizers (Fig. 3i). Subsequently a
banded spherulite pattern, suggesting long-range order, started
to form in some regions of the sample (Fig. 3k), becoming well-
defined by leaving the sample to rest at room temperature
(Fig. 3j and l); the spherulitic domains are characterized by the typ-
ical Maltese crosses, indicating full rotational symmetry, and by a
banded pattern, indicating the twist of crystallites within the
fibres. It is worth noting that, ring-banded and banded spherulite
textures are ascribed to liquid crystals and liquid-crystalline poly-
mers when cooled from the isotropic state [54-60], and not to
supramolecular gels. Although the fibrous network typical of gels
is still present within the sample, the observation of these defined
optical textures was the first clue of the distinction between com-
plex 1 and the above-mentioned parent Ir (III) compounds, the lat-
est being ordered supramolecular metallo-gelators.
Moreover, as for lyotropic liquid crystals, the dried samples
generated by self-evaporation of water from gel phases of complex
1 do not retain any birefringent textures under POM. This beha-
viour stands in stark contrast to that occurring in the true gel
phases generated by the parent compounds previously reported
Ir(III) gels in water [33,35], which preserve in their xerogels their
supramolecular architecture after solvent removal. Indeed, it is
commonly assumed that the xerogel phase preserves quasi-
5

F. Scarpelli, L. Ricciardi, M. La Deda et al.
Journal of Molecular Liquids 334 (2021) 116187
identical supramolecular organization than the relative starting
true gel-phase [41], being the solvent molecules immobilized
within the fibres network merely through surface tension effect.
Conversely, when solvent is removed from a genuine lyome-
sophase, the supramolecular architecture is usually totally or par-
tially destroyed, in the latter case with just loss of some degree of
order, as demonstrated by the signals broadening in the X-Ray
diffraction pattern of the dried-film [61]. Since LLCs undergo their
phase transitions by adding or removing the solvent, in these sys-
tems, the solvents plays a ‘‘structural” role, as well as providing flu-
idity to the system and filling the space around the compounds.
Generally, the orientationally order of lyotropic phases, thus bire-
fringence and characteristic diffraction patterns, can be retained
in a dried film only if the sample in the LC state has been aligned
before solvent evaporation [62-64]. For these reasons, the
supramolecular phase generated by compound 1 in water present
all the features of a true lyotropic liquid crystalline gel phase,
which supramolecular architecture has been elucidated by Powder
X-Ray Diffraction (PXRD) analysis.
nals provides the direct measurement of the phase-change
enthalpy (DH), whose value is ca. 3.0 J/g.
The heating–cooling cycles were repeated three times, demon-
strating the reversibility of the transitions and the stability of the
sample.
The transitions are detectable through DSC up to a mesophase
concentration of 11% w/w. As expected, the transitions exhibit a
decrease of the Tmax values as the concentration decreases. Unfor-
tunately, in the DSC curves of the diluted from 3 to 10% w/w meso-
phases the transitions are no longer detectable (DSC traces at
various concentration are reported in Fig. S8). This could be
explained considering the small quantity of compound present in
these samples with respect to the quantity of water, which proba-
bly renders any transition below the detection limit of the instru-
ment. Note that the DSC trace of the pure complex 1 (Fig. S9) is
absent of any significant signal until thermal degradation, except
maybe for a small change in slope starting at ca. 165 °C that could
be associated with a glass temperature transition. This is typical of
a complete amorphous solid. This observation agrees with the fact
that supramolecular organization occurs only in water as any true
lyotropic system.
4.1. PXRD analysis
4. Thermal analysis
The PXRD analysis was performed on the powder sample, on
the most concentrated mesophase (14% w/w) at room temperature
and at 60 °C, and on the dried film. The PXRD pattern of the pristine
powder, reported in Fig. 5a, shows only broad bands distributed in
a wide 2h range, representative of an amorphous material, without
any long-range order.
Both complexes 1 and 2 are thermally stable until ca. 250 °C,
temperature for which thermal degradation occurs (TGA curves
are reported in Fig. S7).
In order to determine more accurately the temperature of the
phase transitions and the associated enthalpy variation, DSC mea-
surements were carried out, both in diluted and concentrated sam-
ples. The DSC curve of the most concentrated mesophase (14% w/
w), chosen as representative sample, is reported in Fig. 4. The heat-
ing DSC curve of the 14% w/w sample shows an endothermic peak
corresponding to the isotropic transition. This peak presents its
maximum at ca. 49 °C, in perfect agreement with the Ti detected
through POM observation. The cooling DSC curve shows an
exothermic peak, assigned to the isotropy-mesophase transition.
The peak maximum falls at ca. 33 °C, once again in agreement with
the POM observation. Noteworthy, only one transition is observ-
able, indicative of a unique supramolecular organization in water.
Moreover, the two opposite curves present a hysteresis feature,
probably arising from the sluggishness of the exothermic transi-
tion, as reported for many gel phases [36,65] and for liquid-
crystalline phases [66]. Furthermore, the integration of these sig-
Differently from the neat powder diffractogram, the most con-
centrated mesophase (14% w/w), acquired at room temperature
(Fig. 5b), exhibits several well distinguishable reflection peaks,
indicative of a high degree of order. As expected, the PXRD pattern
of the 14% w/w sample in water acquired at 60 °C (Fig. 5c), thus
above its isotropic transition, displays only a broad peak in the
wide-angle range characteristic of an isotropic liquid. Similarly,
the PXRD analysis performed on the dried samples, independently
of the initial concentration in water, corroborates the loss of bire-
fringence seen under POM upon dehydration and all patterns show
the total absence of defined reflection peaks and the presence of
broad halos attributable to a completely amorphous material
(Fig. 5d). Taking into account the high tendency of the complex
to self-assemble into fibrous structures [35], a two-dimensional
columnar organization of [(ppy)2Ir(dpq)]CH3CO2 in the lyotropic
mesophase can be assumed. Therefore the pattern indexation
was performed through LCDixRay program, a free software for
powder diffraction indexing of columnar liquid crystals [67]. It is
worth noting that, due to the lyotropic nature of the sample and
to the presence of a large amount of water, in the mesophase pat-
tern many peaks are broad, poorly resolved and possibly resulting
from the overlap of several reflections. Hence, in order to simplify
the display of separated peaks, simulated patterns with Gaussian
deconvoluted peaks have been conducted and are reported below
the experimental diffractogram (Fig. 6). As shown in Fig. 6, the
indexation suggests the existence of a dual supramolecular archi-
tecture, consisting in tetragonal columns of [(ppy)2Ir(dpq)]CH3CO2
complex, in turn arranged in a larger columnar system with an
oblique symmetry. The first reflection peak presents two shoul-
ders, which reasonably derive from the less intense second and
third peaks, as evidenced by the simulated pattern below; these
three signals can be associated to the d10, d01 and d11 interplanar
distances of a 2-dimensional oblique system (Colo). On the con-
trary, the reflection at 2h = 10.23 (d = 8.48 Å), characterized by a
not negligible intensity, represents the first reflection (d10) of the
second columnar arrangement, which present tetragonal
Fig. 4. DSC traces of the 14% w/w mesophase of [(ppy)2Ir(dpq)]CH3CO2 in water (3
heating–cooling cycles).
6

F. Scarpelli, L. Ricciardi, M. La Deda et al.
Journal of Molecular Liquids 334 (2021) 116187
Fig. 5. PXRD patterns of [(ppy)2Ir(dpq)]CH3CO2: a) powder sample; b) 14% w/w mesophase at room temperature; c) 14% w/w mesophase at 60 °C; d) xerogel.
peaks with high values of miller indices ii) concomitant absence
of numerous peaks with smaller miller indices, iii) unreasonable
difference in peak intensity between the signals. For these reasons,
this solution has been ruled out. The complete indexation of the
[(ppy)2Ir(dpq)]CH3CO2 mesophase PXRD pattern, together with
an in-plane view of the dual supramolecular organization, is
Table 1
Indexation of PXRD spectra of the [(ppy)2Ir(dpq)](CH3CO2) 14% w/w mesophase and
in-plane view of the dual supramolecular organization (inset).
[a]
dobs (Å)
dhk (system)
dcalcd (Å)
Cell parameters
32.81
28.47
22.52
13.49
11.22
10.15
9.33
8.48
8.20
8.05
7.59
7.42
7.20
7.07
6.59
5.96
4.82
4.36
4.22
3.88
3.41
3.23
10 (Colo)
01 (Colo)
11 (Colo)
21 (Colo)
22 (Colo)
31 (Colo)
13 (Colo)
10 (Colt)
40 (Colo)
41 (Colo)
33 (Colo)
42(Colo)
04(Colo)
14(Colo)
50(Colo)
11 (Colt)
45 (Colo)
55 (Colo)
20 (Colt)
21(Colt)
32.81[b]
28.47[b]
22.52[b]
13.50
11.26
10.52
9.34
Colo
ao = 32.94 Å
bo = 28.58 Å
c
= 84.9°
8.48[b]
8.2
Fig. 6. PXRD patterns of the 14% w/w mesophase of [(ppy)2Ir(dpq)]CH3CO2 at room
temperature and the simulated Gaussian peaks deconvolution with relative
indexation.
Colt
at = 8.48 Å
8.08
7.51
7.4
7.12
7.09
6.56
5.99
4.88
symmetry (Colt). A similar dual supramolecular architecture was
observed for the parent compound [(ppy)2Ir(bpy)]EtOCH2CO2
[35], however, in that case, the double columnar organization
was prominently displayed only in the dried films diffractograms.
The necessity to refer to a double organisation to index the PXRD
pattern is due to the presence of 4 reflection peaks in the middle
angle region presenting higher intensity with respect to the other
signals and these 4 diffraction peaks can be indexed as the (10),
(11), (20) and (21), the four first reflection peaks of a tetragonal lat-
tice. Although a possible unique oblique system could be used to
fully index the spectrum, this solution would lead to i) reflection
4.50
4.24
3.79
[a] Calculated data were obtained using LCDixRay program [67].
[b] Data chosen for calculations.
7

F. Scarpelli, L. Ricciardi, M. La Deda et al.
Journal of Molecular Liquids 334 (2021) 116187
reported in Table 1. Noteworthy, in the diffractogram wide-angle
region, characterized by the broad halo, two small shoulders seem
to emerge, with d values of 3.41 and 3.23 Å, respectively. These two
reflections, that would although require more sophisticated elec-
tron diffraction technique to ascertain their existence, could rea-
sonably be attributed to intercolumnar stacking. Indeed, the
results red-shifted with a maximum at 625 nm (due to the high
polarity of the solvent) and extremely weak (Fig. 7b inset and
Table 2), due to the possible hydrogen-bonding interactions
between the nitrogen atoms on the pyrazine ring of the dpq ligand
and water molecules [43,72], as already observed for related
dipyridoquinoxaline complexes [43,73]. This behavior confirms
that the emission is originated from a 3MLCT state [74–76].
By increasing the water solutions concentration (Table 2) from
2 ꢁ 10ꢀ4 to 6.6 ꢁ 10ꢀ2 M (5% w/w) a progressive blue-shift of the
emission maximum (from 632 to 610 nm) associated to a progres-
sive enhancement of the luminescence quantum yield (from 0.05
to 2.1%) are observed. Moreover, all the recorded luminescence
decays turned out to be bi-exponential. The effect of the concentra-
tion increase is twofold: on the one hand, it reduces the exposure
of the complex to the aqueous environment, while on the other it
involves the beginnings of the rigid structure’s formation, precur-
sors of the gel. The progressive change of the molecular environ-
ment and medium rigidity (rigidochromic effect [77]) is
associated to a progressive shift toward higher energy of the 3MLCT
state, while the observed bi-exponential luminescent decays
strictly suggest the presence of aggregation phenomena. The posi-
tive answer to the inverse test tube experiment displayed by sam-
ples from 3% to 14% w/w, is correlated to the increase of this
rigidochromism however, it is only evident onto the photophysical
properties only above 7% w/w when the lifetime decay can be fit by
a monoexponential function. This phenomenon suggests the coex-
istence of at least two types of aggregates for highly diluted gel
phases (3%-7%).
extended and planar ligand dpq might easily interact through
p-
p
interactions with neighbourhood complex molecules, whose
average distance is typically between 3 and 4 Å [68,69]. These
interactions might also explain the self-assembling of the fibres
into larger bundles as previously observed by TEM.
4.2. DFT and photophysics analysis
To provide a quantum chemical insight into the synthesised
complex 1, the Density Functional Theory (DFT) method was
employed investigating the ground-state and excited triplet state
electronic structures and the orbital configurations of the cation
[(ppy)2Ir(dpq)]+. The calculation level of theory employed herein
(B3LYP/LANL2DZ for Ir atoms / 6-31G(d) for all other atoms), has
been widely used throughout the literature for the computational
modelling of both neutral and ionic Ir(III) complexes [70,71].
For the ground state, all the fifth highest occupied molecular
orbitals are denoted to be mainly ppy/metal in character evenly
distributed onto the two ppy ligands and the metal centre, while
the third lowest unoccupied orbitals are almost exclusively dis-
tributed onto the dpq ancillary ligand with a small contribution
of the metal centre. Instead, both the LUMO+3 and LUMO+4 are
distributed on the ppy/metal fragments. A graphical representa-
tion of the two highest occupied and two lowest unoccupied
MOs is reported in Fig. S10.
Indeed, as aforementioned, at a concentration of 5% w/w the
presence of elongated supramolecular assemblies was observed,
with directional intermolecular interactions that reduce the possi-
bility of each single molecule to interact with the solvent mole-
cules and impart rigidity. In support of this, confocal images of
the 5% w/w sample are carried out and reported in Fig. 8. These
images show the presence of luminescent wire-shaped superstruc-
tures, already observed under optical microscope. When excited at
488 nm, these structures showed an intense emission and the pres-
ence of three-dimensional fiber bundles.
The electronic absorption spectra of complex 1 in CH2Cl2 and in
water solution in high dilution conditions are shown in Fig. 7a.
Similar features have been recorded for 2 and results are present-
ing in Fig. S11 and Table S1. In both solvents, 1 displays intense
absorption bands between 250 and 300 nm assigned to spin-
allowed N^N and C^N intraligand (1LC;
p ? p*) transitions
[43,71]. At lower energies, from 340 to 450 nm, less intense
absorption bands are observed, attributable to a mixture of
spin-allowed metal-to-ligand and ligand-to-ligand charge transfer
(1MLCT, 1LLCT) transitions in good agreement with DFT
calculations and consistent with the reported assignments for the
analogous complex [(ppy)2Ir(dpq)]PF6 in acetonitrile solution
[71]. Upon photoexcitation, complex 1 in CH2Cl2 diluted solution
exhibits an orange emission centered at 600 nm (Fig. 7b), with
an emission quantum yield of 6.7% and an excited-state lifetime
of 162 ns (Table 2).The emission of 1 in diluted water solution
A plateau of the photophysical properties values of 1 is
observed in the 7–11% concentration range: the emission peak is
fixed at 613 nm, the emission quantum yield shows the value of
4.8%, while the luminescence intensity decay is deconvoluted by
a
monoexponential function with a lifetime value of about
256 ns (Table 2). In this range of concentration, the photophysical
properties are governed by the supramolecular organization of the
gel. However, at the concentration of 14% w/w, the emission yield
drops slightly and the lifetime is reduced; noticeably, the
80000
500
b)
a)
160
140
120
400
100
80
60000
40000
20000
0
60
300
40
500
550
600
650
700
200
100
0
250
300
350
400
450
500
500
550
600
650
700
750
800
Wavelength (nm)
Wavelength (nm)
Fig 7. a) Electronic absorption spectra of 1 in CH2Cl2 (black line) and in water (red line) solution at room temperature, b) Emission spectra of 1 in CH2Cl2 (black line) and in
water solution (5 ꢁ 10ꢀ6 M, red line) at room temperature (excitation wavelength: 400 nm). The inset shows the magnified emission spectrum of 1 in water solution (emission
intensity ꢂ 100).
8

F. Scarpelli, L. Ricciardi, M. La Deda et al.
Journal of Molecular Liquids 334 (2021) 116187
Table 2
Photophysical data of complex 1 in solution at room temperature.
Solvent
Mol.Lꢀ1
w/w (%)
Emission, kmax/nm
U (%)
Lifetime, s/ns (a/%)
CH2Cl2
H2O
H2O
H2O
H2O
H2O
H2O
H2O
H2O
5 ꢁ 10ꢀ6
0.0004
0.0004
0.016
0.16
1.56
5
7
9
11
600
625
632
632
618
610
613
613
613
6.7
161.9
–
5 ꢁ 10ꢀ6
<0.02
0.05
0.3
1.1
2.1
4.9
4.8
4.8
2 ꢁ 10ꢀ4
4.9 (17.03), 53 (82.97)
10.3 (50.49), 59.6 (49.51)
29.1 (47.11), 116.5 (52.89)
37 (53.71), 156.8 (46.29)
259.7
2 ꢁ 10ꢀ3
2 ꢁ 10ꢀ2
6.6 ꢁ 10ꢀ2
9.5 ꢁ 10ꢀ2
1.25 ꢁ 10ꢀ1
1.56 ꢁ 10ꢀ1
256.9
256.6
perfect reversibility in restoring the ordered phase as the temper-
ature decreases (Fig. 9a).
The photophysical features of 1 were explored in its xerogel
form. The sample shows a luminescence band peaked at 623 nm
(Fig. 9b and Table 3), almost superimposable to that observed for
the gel at 55 °C. Taking into account that the emission intensity
decay follows a bi-exponential trend, we can conclude that, simi-
larly to what has been observed by increasing the temperature,
there is loss of the positional order - as evidenced by the XRD spec-
tra - and an attenuation of the rigidochromism. However, the
quantum yield and the lifetime value are considerably higher in
the xerogel respect to the gel at 55 °C; this is due both to the lack
of thermal agitation, but also, and above all, to the loss of water
molecules, which, as we have seen above, constitute a detriment
to the emission.
Finally, for completeness, the photophysical characterization of
1 in the solid state was carried out and the emission spectrum and
the related data reported in Fig. S12 and Table S2, respectively. The
photophysical data indicate that the interactions between the
chromophores are similar to those observed in the xerogel,
although the presence of co-crystallization water probably causes
a slight decrease in the lifetime and emission quantum yield.
Fig 8. Confocal images of the 5% w/w mesophase originated by 1 in water. Scale
bar: 75 m.
l
excited-state intensity decay still following a monoexponential
trend and the maximum emission is even more blue-shifted
(kem = 605 nm), confirming a greater rigidochromism (Table 3).
These two factors could be correlated to a higher degree of inter-
chromophoric contacts with respect to the less concentrated sam-
ples, initiating a quenching of the emission.
5. Conclusions
In this work, we have reported the first example of an one-
component luminescent lyotropic liquid crystalline gel based on
a Ir(III) complex. The compound described herein, [(ppy)2Ir(dpq)]
CH3CO2, is able to generate a viscous mesophase in water on a
large range of concentration from 3% to 14% w/w, with the forma-
tion of supramolecular fibre-shaped aggregates on the micrometre
scale. The lyomesophase is characterized by a banded spherulite
texture and by a double columnar organization, elucidated by its
PXRD pattern indexation, consisting of tetragonal columns of
[(ppy)2Ir(dpq)]CH3CO2 complex, which in turn self-organize in
an oblique columnar system. Compared to the previously reported
parent compound [(ppy)2Ir(bpy)]EtOCH2CO2 [35], we demon-
strated that the expansion of the aromaticity of the N^N ancillary
ligand leads to the generation of a true lyotropic behaviour. It is
important to emphasize that the formation of these supramolecu-
lar phases requires a delicate balance between solubilization and
aggregation, since a further aromaticity extension, provided by
The effects of the temperature onto the emission spectra, lumi-
nescence quantum yields and lifetimes of the 14% w/w gel phase
sample were investigated. The sample was heated repeatedly from
room temperature up to 55 °C - temperature well beyond the iso-
tropic transition, for several cycles (Fig. 9a and Table 3). As clearly
shown in Fig. 9a, the temperature increase leads to a red-shift of
the emission band peak from 605 to 625 nm, and a decrease of
the luminescence quantum yield (/) and lifetimes. After cooling,
the spectral position and all photophysical values are re-
established, confirming the reversibility of the transitions and the
stability of the sample. This behavior confirms that, by increasing
the temperature, effects of rigidochromism are attenuated, with
the consequent red-shift of the emission which must be fitted with
a bi-exponential function. The thermal motions allowed in the iso-
tropic phase increase the non-radiative constant rate, leading to a
decrease of the emission quantum yield. It should be noted the
Table 3
Photophysical data of 1 in 14% w/w gel phase at different temperature and after solvent evaporation (xerogel).
Sample
Temperature
(°C)
Emission, kmax (nm)
U (%)
Lifetime,
167.5
23.1(63.97), 104.1(36.03)
165.3
s/ns (a/%)
14% w/w
14% w/w
14% w/w (after cooling)
14% w/w xerogel
25
55
25
25
605
625
605
623
4.3
2.4
4.5
10.7
75.8(22.26), 207.9(77.74)
9

F. Scarpelli, L. Ricciardi, M. La Deda et al.
Journal of Molecular Liquids 334 (2021) 116187
1000
a)
b)
8000
6000
4000
2000
0
25°C
55°C
25°C
750
500
250
0
550
600
650
700
750
800
550
600
650
700
750
800
Wavelength (nm)
Wavelength (nm)
Fig. 9. a) Emission spectra of 1 in 14% w/w gel phase at different temperature (excitation wavelength: 400 nm), b) Emission spectrum of the xerogel formed from1 (excitation
wavelength: 400 nm).
the use of dppz ligand, results in an almost insoluble compound.
The long-range orientational order and the fibrous network of
the supramolecular phase generated by [(ppy)2Ir(dpq)]CH3CO2 in
water might lay the groundwork for the development of other lyo-
tropic liquid crystals metallogels addressed to specific applications.
In this light, we also demonstrated, through this example, that for
LLCGs containing luminophores, the luminescent properties are
deeply correlated with the supramolecular order and that they
can be finely tuned depending on the concentration and tempera-
ture. Indeed, while emission quenching in water under high dilu-
tion conditions is observed, when the gel starts to form, emission
is repristinated. The observed behavior of the variation in emission
quantum yield and position of the emission band peak, highly
depends on both concentration and temperature. These effects
are to be correlated both to the supramolecular organisation of
the LLCGs, and the temperature range in which lyotropic phase
occurs. When the isotropic temperature is reached, free motion
and reduction of rigidity of the phase induces an increase of the
non-radiative constant rate, hence a decrease of intensity of emis-
sion. Highly noticeable, we demonstrated the complete reversibil-
ity of the transition from LLCG to isotropic liquid (and vice versa),
both in supramolecular organization and in photophysical proper-
ties. These findings might open the door to the use of this new class
of materials for smart devices.
7.73 (m, 4H), 7.51 (d, J = 5.7 Hz, 2H), 7.13–6.96 (m, 6H), 6.40 (d,
J = 6.9 Hz, 2H). IR (KBr/cmꢀ1): 3367, 3035, 2956, 2917, 1728,
1605, 1581, 1476, 1437.
5.3. Synthesis of [(ppy)2Ir(dpq)]CH3CO2 (1)
Intermediate IIa (150 mg, 0.195 mmol) and silver acetate
(35.6 mg, 0.215 mmol) were refluxed in the dark in ca. 40 ml of
MeOH. After 4 h the suspension, once cooled down to temperature,
was filtered through celite in order to remove AgCl. The solution
was evaporated and n-hexane was added. An orange powder was
recovered through filtration. Yield (75%, 115 mg). M.p. (dec.) > 250
°C. Anal. calcd for [C38H27IrN6O2] (MW 792.2 g molꢀ1): C: 57.64, H:
3.44, N: 10.61%; found C: 57.18, H: 3.54, N: 10.01%. 1H NMR
(300 MHz, CDCl3, TMS), d (ppm): 9.75 (d, J = 7.8, 2H), 9.20 (s,
2H), 8.40 (d, J = 4.2 Hz, 2H), 8.10 (q, J = 5.4 Hz, 2H), 7.95 (d,
J = 8.1, 2H), 7.80–7.73 (m, 4H), 7.46 (d, J = 5.7 Hz, 2H), 7.13–6.96
(m, 6H), 6.40 (d, J = 7.2 Hz, 2H), 1.86 (s, 3H). IR (KBr/cmꢀ1):
3411, 3040, 2961, 2857, 1605, 1581, 1477, 1437, 1404.
5.4. Synthesis of dppz ligand
Ligand dppz was synthesis through a two steps procedure start-
ing from 1,10-phenenthroline oxidised in 1,10-phenanthroline-
5,6-dione, which was in turn reacted with benzene-1,2-diamine.
All general equipment and procedures are reported in supple-
mentary materials (ESI).
5.5. Synthesis of 1,10-phenanthroline-5,6-dione
5.1. Synthesis of precursor [(ppy)2Ir(
l-Cl)]2 (I)
1,10-phenanthroline-5,6-dione was prepared following the
method of Gillard et al. [78] An ice-cold mixture of conc. sulphuric
acid (20 ml) and conc. nitric acid (10 ml) was slowly added to 1,10-
phenanthroline (2 g, 10 mmol) and potassium bromide (2 g,
17 mmol). The red mixture was refluxed (150 °C) for 3 h in which
time the solution turned to a yellow colour. The hot yellow solu-
tion was then poured over ice and neutralised using a saturated
solution of sodium hydroxide. The solution was then filtered,
extracted with CH2Cl2 and evaporated to dryness. Recrystallisation
from hot ethanol, yielded a yellow powder. Yield (66%, 1.39 g).
Anal. Calcd. for [C12H6N2O2] (MW 210.2 g molꢀ1): C, 68.57; H,
2.88, N, 13.33; found: C, 68.29; H, 2.93, N, 13.45. 1H NMR
(300 MHz, CDCl3, TMS), d (ppm): 9.13 (dd, J = 4.5 Hz, J = 1.8, 2H),
8.51 (dd, J = 8.7 Hz, J = 1.8, 2H), 7.59 (q, J = 6.0 Hz, 2H). IR (KBr/
cmꢀ1): 3535, 3425, 3061, 1983, 1703, 1681, 1576, 1560,1459.
The synthesis of the precursor [(ppy)2Ir(
formed through a microwave assisted reaction, as reported in ref.
[33].
l
-Cl)]2 (I) was per-
5.2. Synthesis of [(ppy)2Ir(dpq)]Cl (IIa)
To ca. 45 ml of hot and degassed CH2Cl2 was added intermedi-
ate I (200 mg, 0.186 mmol). Concomitantly, to ca. 15 ml of hot and
degassed MeOH was added the ancillary ligand dipyridinoquinox-
aline (dpq) (86.6 mg, 0.372 mmol). After mixing up the two solu-
tions, a clear orange solution was obtained. The reaction mixture
was refluxed under inert atmosphere. After 24 h solvents were
evaporated through rotavapor and a yellow precipitate was recov-
ered by addition of petroleum ether, followed by filtration. Yield
(96%, 285 mg). M.p. > 250 °C. Anal. calcd for [C36H24ClIrN6] (MW
768.3 g molꢀ1): C: 56.28, H: 3.15, N: 10.94%; found C: 56.13, H:
3.34, N: 10.87%. 1H NMR (300 MHz, CDCl3, TMS), d (ppm): 9.76
(dd, JD = 8.4 Hz, Jd = 1.8, 2H), 9.20 (s, 2H), 8.41 (dd, JD = 6.6 Hz,
Jd = 1.5, 2H), 8.14 (q, J = 5.1 Hz, 2H), 7.95 (d, J = 7.8, 2H), 7.79–
5.6. Synthesis of dipyridophenazine (dppz)
dppz was prepared following the procedure reported by Wang
et al. [79] A mixture of 1,10-phenanthroline-5,6-dione (210.2 mg,
10

F. Scarpelli, L. Ricciardi, M. La Deda et al.
Journal of Molecular Liquids 334 (2021) 116187
gel formation, J. Mater. Chem. C. 8 (2020) 5335–5348, https://doi.org/10.1039/
d0tc00561d.
[2] A. Seeboth, H. Holzbauer, The optical behavior of lyotropic liquid crystalline
polymer gel networks: dependence on temperature, Adv. Mater. (1996) 408–
411, https://doi.org/10.1002/adma.19960080507.
[3] F.A. Aouada, M.R. de Moura, A.F. Rubira, E.C. Muniz, P.R.G. Fernandes, H. Mukai,
A.C.F. da Silveira, R. Itri, Birefringent hydrogels based on PAAm and lyotropic
liquid crystal: optical, morphological and hydrophilic characterization, Eur.
1 mmol), benzene-1,2-diamine (119 mg, 1.1 mmol), 10 ml of etha-
nol, and 4-methylbenzenesulfonic acid (1.9 mg, 0.01 mmol) was
refluxed for 12 h. The crude product was filtered off and then
recrystallized from ethanol to give the pure desired product. Yield
(64%, 180 mg). Anal. Calcd. for [C18H10N4] (MW 282 g/mol): C,
76.58; H, 3.57, N, 19.85; found: C, 76.16; H, 3.75, N, 19.22. 1H
NMR (300 MHz, CDCl3, TMS), d (ppm): 9.67 (dd, JD = 7.5 Hz,
Jd = 1.8, 2H), 9.29 (dd, JD = 4.0 Hz, Jd = 1.8, 2H), 8.40–8.36 (m,
2H), 7.96–7.92 (m, 2H), 7.83–7.79 (m, 2H).
Polym.
J.
42
(2006)
2781–2790,
https://doi.org/10.1016/j.
eurpolymj.2006.04.009.
[4] S. Dieterich, T. Sottmann, F. Giesselmann, Gelation of lyotropic liquid-crystal
phases-the interplay between liquid crystalline order and physical gel
formation, Langmuir 35 (2019) 16793–16802, https://doi.org/10.1021/acs.
langmuir.9b02621.
[5] K. Steck, J.H. Van Esch, D.K. Smith, C. Stubenrauch, Tuning gelled lyotropic
liquid crystals (LLCs)-probing the influence of different low molecular weight
gelators on the phase diagram of the system H 2 O/NaCl-Genapol LA070, Soft
Matter. 15 (2019) 3111–3121, https://doi.org/10.1039/c8sm02330a.
[6] Y. Xu, M. Laupheimer, N. Preisig, T. Sottmann, C. Schmidt, C. Stubenrauch,
Gelled lyotropic liquid crystals, Langmuir 31 (2015) 8589–8598, https://doi.
org/10.1021/acs.langmuir.5b01992.
[7] H.E. Warriner, S.H.J. Idziak, N.L. Slack, P. Davidson, C.R. Safinya, Lamellar
biogels: fluid-membrane-based hydrogels containing polymer lipids, Science
(80-.) 271 (1996) 969–973, doi: 10.1126/science.271.5251.969.
[8] K. Hiltrop, Lyotropic liquid crystals, in: Liq. Cryst., Steinkopff, Heidelberg, 1994,
pp. 143–171, doi: 10.1007/978-3-662-08393-2_4.
[9] V.K. Singh, K. Pal, I. Banerjee, K. Pramanik, A. Anis, S.M. Al-Zahrani, Novel
organogel based lyotropic liquid crystal physical gels for controlled delivery
applications, Eur. Polym. J. 68 (2015) 326–337, https://doi.org/10.1016/j.
eurpolymj.2015.05.009.
[10] M. Ilyas, M.A. Haque, Y. Yue, T. Kurokawa, T. Nakajima, T. Nonoyama, J.P. Gong,
Water-triggered ductile-brittle transition of anisotropic lamellar hydrogels
and effect of confinement on polymer dynamics, Macromolecules 50 (2017)
8169–8177, https://doi.org/10.1021/acs.macromol.7b01438.
[11] K. Mito, M.A. Haque, T. Nakajima, M. Uchiumi, T. Kurokawa, T. Nonoyama, J.P.
Gong, Supramolecular hydrogels with multi-cylindrical lamellar bilayers:
Swelling-induced contraction and anisotropic molecular diffusion, Polymer
(Guildf) 128 (2017) 373–378, https://doi.org/10.1016/j.polymer.2017.01.038.
[12] A. Heeres, C. Van Der Pol, M. Stuart, A. Friggeri, B.L. Feringa, J. Van Esch,
Orthogonal self-assembly of low molecular weight hydrogelators and
surfactants, J. Am. Chem. Soc. 125 (2003) 14252–14253, https://doi.org/
10.1021/ja036954h.
[13] S.A. Willis, G.R. Dennis, G. Zheng, W.S. Price, Preparation and physical
properties of a macroscopically aligned lyotropic hexagonal phase templated
hydrogel, React. Funct. Polym. 73 (2013) 911–922, https://doi.org/10.1016/j.
reactfunctpolym.2013.02.008.
5.7. Synthesis of [(ppy)2Ir(dppz)]Cl (IIb)
To ca. 40 ml of hot and degassed CH2Cl2 was added [(ppy)2Ir(l-
Cl)]2 (I) (170 mg, 0.16 mmol). At the same time, to ca. 12 ml of hot
and degassed MeOH was added the ancillary ligand dppz (89.6 mg,
0.32 mmol). After mixing up the two solutions, a clear orange solu-
tion was obtained. This solution was refluxed under inert atmo-
sphere. After 24 h, solvents were evaporated through rotavapor
and a yellow precipitate was recovered by addition of petroleum
ether, followed by filtration. Yield (95%, 248 mg). M.p. > 250 °C.
Anal. calcd for [C40H26ClIrN6] (MW 818.2 g molꢀ1): C: 58.71, H:
3.20, N: 10.27%; found C: 58.13, H: 3.444, N: 10.81%. 1H NMR
(300 MHz, CDCl3, TMS), d (ppm): 9.91 (d, J = 7.0 Hz, 2H), 8.47–
8.38 (m, 4H), 8.18–8.14 (m, 2H), 8.07–8.04 (m, 2H), 7.96 (d,
J = 7.8, 2H), 7.80–7.74 (m, 4H), 7.58 (d, J = 5.7 Hz, 2H), 7.13–6.97
(m, 6H), 6.41 (d, J = 6.9 Hz, 2H). IR (KBr/cmꢀ1): 3401, 3042, 2912,
2329, 1605, 1583, 1558, 1477.
5.8. Synthesis of [(ppy)2Ir(dppz)]CH3CO2 (2)
Intermediate IIb (100 mg, 0.12 mmol) and silver acetate
(22.3 mg, 0.13 mmol) were refluxed in ca. 20 ml of MeOH, repaired
from light. After 4 h the suspension was filtered through celite in
order to remove AgCl. The solution was concentrated through
rotavapor and diethyl ether was added. A yellow powder was
recovered through filtration. Yield (74%, 75 mg). M.p.(dec) > 250 °C.
Anal. calcd for [C42H29IrN6O2] (MW 842.2 g molꢀ1): C: 59.92, H:
3.47, N: 9.98%; found C: 59.33, H: 3.52, N: 10.02%. 1H NMR
(300 MHz, CDCl3, TMS), d (ppm): 9.90 (dd, JD = 9.0 Hz, Jd = 1.5 Hz,
2H), 8.48–8.38 (m, 4H), 8.14–8.04 (m, 4H), 7.96 (d, J = 8.1 Hz, 2H),
7.81–7.74 (m, 4H), 7.54 (d, J = 5.1 Hz, 2H), 7.13–6.97 (m, 6H), 6.41
(d, J = 6.9 Hz, 2H), 1.84 (s, 3H). IR (KBr/cmꢀ1): 3399, 3041, 2923,
2329, 1606, 1582, 1561, 1419.
[14] M. Laupheimer, N. Preisig, C. Stubenrauch, The molecular organogel n-decane/
12-hydroxyoctadecanoic acid: sol-gel transition, rheology, and microstructure,
Colloids Surfaces A Physicochem. Eng. Asp. 469 (2015) 315–325, https://doi.
org/10.1016/j.colsurfa.2015.01.039.
[15] B.O. Okesola, V.M.P. Vieira, D.J. Cornwell, N.K. Whitelaw, D.K. Smith, 1,3:2,4-
Dibenzylidene-d-sorbitol (DBS) and its derivatives-efficient, versatile and
industrially-relevant low-molecular-weight gelators with over 100 years of
history and a bright future, Soft Matter. 11 (2015) 4768–4787, https://doi.org/
10.1039/c5sm00845j.
[16] C.C. Lin, K.S. Anseth, PEG hydrogels for the controlled release of biomolecules
in regenerative medicine, Pharm. Res. 26 (2009) 631–643, https://doi.org/
10.1007/s11095-008-9801-2.
[17] C. Stubenrauch, F. Gießelmann, Gelled complex fluids: combining unique
structures with mechanical stability, Angew. Chemie - Int. Ed. 55 (2016) 3268–
3275, https://doi.org/10.1002/anie.201506603.
Declaration of Competing Interest
[18] T. Kato, Y. Hirai, S. Nakaso, M. Moriyama, Liquid-crystalline physical gels,
Chem. Soc. Rev. 36 (2007) 1857–1867, https://doi.org/10.1039/b612546h.
[19] P.B. Geraghty, D. Attwood, J.H. Collett, Y. Dandiker, The in vitro release of some
antimuscarinic drugs from monoolein/water lyotropic liquid crystalline gels,
Pharm. Res. 13 (1996) 1265–1271, https://doi.org/10.1023/A:1016036908947.
[20] R. Ivanova, B. Lindman, P. Alexandridis, Effect of pharmaceutically acceptable
glycols on the stability of the liquid crystalline gels formed by poloxamer 407
in water, J. Colloid Interface Sci. 252 (2002) 226–235, https://doi.org/10.1006/
jcis.2002.8417.
[21] S.Z.D. Cheng, S.K. Lee, J.S. Barley, S.L.C. Hsu, F.W. Harris, Gel/sol and liquid-
crystalline transitions in solution of a rigid-rod polyimide, Macromolecules 24
(1991) 1883–1889, https://doi.org/10.1021/ma00008a028.
[22] B. Bai, H. Wang, H. Xin, F. Zhang, B. Long, X. Zhang, S. Qu, M. Li, Hydrazide-
based organogels and liquid crystals with columnar order, New J. Chem. 31
(2007) 401–408, https://doi.org/10.1039/b614444f.
[23] G.C. Kuang, X.R. Jia, M.J. Teng, E.Q. Chen, W.S. Li, Y. Ji, Organogels and liquid
crystalline properties of amino acid-based dendrons: a systematic study on
structure-property relationship, Chem. Mater. 24 (2012) 71–80, https://doi.
org/10.1021/cm201913p.
[24] G.C. Kuang, Y. Ji, X.R. Jia, Y. Li, E.Q. Chen, Y. Wei, Self-assembly of amino-acid-
based dendrons: organogels and lyotropic and thermotropic liquid crystals,
Chem. Mater. 20 (2008) 4173–4175, https://doi.org/10.1021/cm8006952.
[25] M.A. Firestone, J.A. Dzielawa, P. Zapol, L.A. Curtiss, S. Seifert, M.L. Dietz,
Lyotropic liquid-crystalline gel formation in a room-temperature ionic liquid,
Langmuir 18 (2002) 7258–7260, https://doi.org/10.1021/la0259499.
The authors declare that they have no known competing finan-
cial interests or personal relationships that could have appeared
to influence the work reported in this paper.
Acknowledgements
Part of this work was supported by the Ministero dell’Istru-
zione, dell’Università e della Ricerca through PON 2007/2013 ELIO-
TROPO (PON03PE_00092_2).
Appendix A. Supplementary material
Supplementary data to this article can be found online at
https://doi.org/10.1016/j.molliq.2021.116187.
References
[1] K. Steck, S. Dieterich, C. Stubenrauch, F. Giesselmann, Surfactant-based
lyotropic liquid crystal gels - the interplay between anisotropic order and
11

F. Scarpelli, L. Ricciardi, M. La Deda et al.
Journal of Molecular Liquids 334 (2021) 116187
[26] N. Cheng, Q. Hu, Y. Bi, W. Xu, Y. Gong, L. Yu, Gels and lyotropic liquid crystals:
using an Imidazolium-Based catanionic surfactant in binary solvents,
Langmuir 30 (2014) 9076–9084, https://doi.org/10.1021/la502024a.
[27] D. Zhang, Q. Liu, R. Visvanathan, M.R. Tuchband, G.H. Sheetah, B.D. Fairbanks,
N.A. Clark, I.I. Smalyukh, C.N. Bowman, A supramolecular hydrogel prepared
[49] Y.J. Yadav, B. Heinrich, G. De Luca, A.M. Talarico, T.F. Mastropietro, M. Ghedini,
B. Donnio, E.I. Szerb, Chromonic-like physical luminescent gels formed by
ionic octahedral iridium(iii) complexes in diluted water solutions, Adv. Opt.
Mater. 1 (2013) 844–854, https://doi.org/10.1002/adom.201300236.
[50] J. Tanaka, Evaluation of gel point, Gels Handb. (2001) 51–64, https://doi.org/
10.1016/b978-012394690-4/50078-5.
from
a thymine-containing artificial nucleolipid: study of assembly and
lyotropic mesophases, Soft Matter. 14 (2018) 7045–7051, https://doi.org/
10.1039/c8sm01383g.
[28] X.Q. Li, X. Zhang, S. Ghosh, F. Würthner, Highly fluorescent lyotropic
mesophases and organogels based on J-aggregates of core-twisted perylene
bisimide dyes, Chem. - A Eur. J. 14 (2008) 8074–8078, https://doi.org/10.1002/
chem.200800915.
[29] N. Koine, M. Iida, T. Sakai, N. Sakagami, S. Kaizaki, The novel lyotropic liquid
crystalline phase of the dinuclear metal complex Na[Cr2(L-tart2H)(phen)2], J.
Chem. Soc. Chem. Commun. (1992) 1714–1716, https://doi.org/10.1039/
C39920001714.
[30] T. Imae, Y. Ikeda, M. Iida, N. Koine, S. Kaizaki, Self-organization of a dinuclear
metal complex in lyotropic liquid crystal: ribbonlike supramolecular
assemblies, Langmuir. 14 (1998) 5631–5632, https://doi.org/10.1021/
la9800194.
[31] B. Donnio, Lyotropic metallomesogens, Curr. Opin. Colloid Interface Sci. 7
(2002) 371–394, https://doi.org/10.1016/S1359-0294(02)00084-5.
[32] D. Rota Martir, E. Zysman-Colman, Supramolecular iridium(III) assemblies,
Coord. Chem. Rev. 364 (2018) 86–117, https://doi.org/10.1016/j.
ccr.2018.03.016.
[33] F. Scarpelli, A. Ionescu, L. Ricciardi, P. Plastina, I. Aiello, M. La Deda, A. Crispini,
M. Ghedini, N. Godbert, A novel route towards water-soluble luminescent
iridium(III) complexes: Via a hydroxy-bridged dinuclear precursor, Dalt. Trans.
45 (2016) 17264–17273, https://doi.org/10.1039/c6dt02976k.
[34] C.O. Rossi, C. Cretu, L. Ricciardi, A. Candreva, M. La Deda, I. Aiello, M. Ghedini, E.
I. Szerb, Rheological and photophysical investigations of chromonic-like
supramolecular mesophases formed by luminescent iridium(III) ionic
complexes in water, Liq. Cryst. 44 (2017) 880–888, https://doi.org/10.1080/
02678292.2016.1254294.
[51] Y. Ikeda, T. Imae, M. Iida, N. Koine, S. Kaizaki, Effect of counterions on the
ribbonlike supramolecular assembly formation of dinuclear metal complexes
in the lyotropic mesophase, Langmuir 17 (2001) 361–368, https://doi.org/
10.1021/la000488h.
[52] M. George, R.G. Weiss, Molecular organogels. Soft matter comprised of low-
molecular-mass organic gelators and organic liquids, Acc. Chem. Res. 39
(2006) 489–497, https://doi.org/10.1021/ar0500923.
[53] M. Lescanne, A. Colin, O. Mondain-Monval, F. Fages, J.L. Pozzo, Structural
aspects of the gelation process observed with low molecular mass
organogelators, Langmuir 19 (2003) 2013–2020, https://doi.org/10.1021/
la026660u.
[54] E.M. Woo, S. Nurkhamidah, Y.F. Chen, Surface and interior views on origins of
two types of banded spherulites in poly(nonamethylene terephthalate), Phys.
Chem. Chem. Phys. 13 (2011) 17841–17851, https://doi.org/10.1039/
c1cp22249j.
[55] J.L. Hutter, J. Bechhoefer, Banded spherulitic growth in a liquid crystal, J. Cryst.
Growth. 217 (2000) 332–343, https://doi.org/10.1016/S0022-0248(00)00479-
6.
[56] I.W. Hamley, Liquid crystal phase formation by biopolymers, Soft Matter. 6
(2010) 1863–1871, https://doi.org/10.1039/b923942a.
[57] Z. Liu, X. Fu, L. Jiang, B. Wu, J. Wang, J. Lei, Solvent-free synthesis and
properties of novel solid-solid phase change materials with biodegradable
castor oil for thermal energy storage, Sol. Energy Mater. Sol. Cells. 147 (2016)
177–184, https://doi.org/10.1016/j.solmat.2015.12.009.
[58] M. Gupta, V. Pal, S.K. Pal, Photo-responsive liquid crystals derived from
azobenzene centered cholesterol-based tetramers, New J. Chem. 42 (2018)
8765–8772, https://doi.org/10.1039/c7nj05142e.
[59] N. Aeinleng, S. Songkro, K. Noipha, T. Srichana, Physicochemical performances
of indomethacin in cholesteryl cetyl carbonate liquid crystal as a transdermal
dosage, AAPS PharmSciTech. 13 (2012) 513–521, https://doi.org/10.1208/
s12249-012-9768-5.
[35] F. Scarpelli, A. Ionescu, I. Aiello, M. La Deda, A. Crispini, M. Ghedini, E. Brunelli,
S. Sesti, N. Godbert, High order in a self-assembled iridium(III) Complex
gelator towards nanostructured IrO2 thin films, Chem. - Asian J. 12 (2017)
2703–2710, https://doi.org/10.1002/asia.201700930.
[60] L.N. Borgheti-Cardoso, F.T.M. de C. Vicentini, T. Gratieri, M.V.L.B. Bentley,
[36] M. Moniruzzaman, P.R. Sundararajan, Low molecular weight organogels based
on long-chain carbamates, Langmuir 21 (2005) 3802–3807, https://doi.org/
10.1021/la047449g.
Liquid crystalline systems containing vitamin E TPGS for the controlled
transdermal nicotine delivery, Brazilian J. Pharm. Sci. 52 (2016) 191–200, doi:
10.1590/S1984-82502016000100021.
[37] V.C. Edelsztein, A.S. Mac Cormack, M. Ciarlantini, P.H. Di Chenna, Self-
assembly of 2, 3-dihydroxycholestane steroids into supramolecular
[61] Y. Chen, Z. Zhao, Z. Bian, R. Jin, C. Kang, X. Qiu, H. Guo, Z. Du, L. Gao, Hexagonal
lyotropic liquid crystal from simple ‘‘Abiotic” foldamers, ChemistryOpen 5
(2016) 386–394, https://doi.org/10.1002/open.201600007.
organogels as
a soft template for the in-situ generation of silicate
nanomaterials, Beilstein J. Org. Chem. 9 (2013) 1826–1836, https://doi.org/
10.3762/bjoc.9.213.
[38] T. Patra, A. Pal, J. Dey, Journal of colloid and interface science birefringent
physical gels of N - (4- n -alkyloxybenzoyl) - L -alanine amphiphiles in organic
solvents: the role of hydrogen-bonding, J. Colloid Interface Sci. 344 (2010) 10–
20, https://doi.org/10.1016/j.jcis.2009.12.003.
[39] A. Kishimura, T. Yamashita, T. Aida, Phosphorescent organogels via
‘‘metallophilic” interactions for reversible RGB-color switching, J. Am. Chem.
Soc. 127 (2005) 179–183, https://doi.org/10.1021/ja0441007.
[62] T. Schneider, A. Golovin, J.C. Lee, O.D. Lavrentovich, Lyotropic chromonic liquid
crystals in aligned films for applications as polarizing coatings, J. Inf. Disp. 5
(2004) 27–38, https://doi.org/10.1080/15980316.2004.9651946.
[63] J.F. Dreyer, Light polarization from films of lyotropic nematic liquid crystals, Le
J. Phys. Colloq. 30 (1969) C4-114–C4-116, doi: 10.1051/jphyscol:1969427.
[64] K.V. Kaznatcheev, P. Dudin, O.D. Lavrentovich, A.P. Hitchcock, X-ray
microscopy study of chromonic liquid crystal dry film texture, Phys. Rev. E -
Stat. Nonlinear, Soft Matter Phys. 76 (2007) 1–14, https://doi.org/10.1103/
PhysRevE.76.061703.
[40] J.H. Jung, G. John, M. Masuda, K. Yoshida, S. Shinkai, T. Shimizu, Self-assembly
of a sugar-based gelator in water: its remarkable diversity in gelation ability
and aggregate structure, Langmuir 17 (2001) 7229–7232, https://doi.org/
10.1021/la0109516.
[65] H. Basit, A. Pal, S. Sen, S. Bhattacharya, Two-component hydrogels comprising
fatty acids and amines: structure, properties, and application as a template for
the synthesis of metal nanoparticles, Chem. - Eur. J. 14 (2008) 6534–6545,
https://doi.org/10.1002/chem.200800374.
[41] I. Muñoz Resta, V. Manzano, F. Cecchi, C. Spagnuolo, F. Cukiernik, P. Di Chenna,
[66] J.K. Vij, I. Prigogine, S.A. Rice, Advances in liquid crystals : a special volume, vol.
113, 2009.
Supramolecular assembly of pH-sensitive triphenylene derived p-gelators and
their application as molecular template for the preparation of silica nanotubes,
Gels 2 (2016) 7, https://doi.org/10.3390/gels2010007.
[67] N. Godbert, A. Crispini, M. Ghedini, M. Carini, F. Chiaravalloti, A. Ferrise,
LCDiXRay:
a user-friendly program for powder diffraction indexing of
[42] K.K.W. Lo, K.Y. Zhang, Iridium(III) complexes as therapeutic and bioimaging
reagents for cellular applications, RSC Adv. 2 (2012) 12069–12083, https://doi.
org/10.1039/c2ra20967e.
[43] K.K.W. Lo, C.K. Chung, N. Zhu, Nucleic acid intercalators and avidin probes
derived from luminescent cyclometalated iridium(III)-dipyridoquinoxaline
and -dipyridophenazine complexes, Chem. - A Eur. J. 12 (2006) 1500–1512,
https://doi.org/10.1002/chem.200500885.
[44] M. Kaller, C. Deck, A. Meister, G. Hause, A. Baro, S. Laschat, Counterion effects
on the columnar mesophases of triphenylene substituted [18]crown-6 ethers:
Is flatter better?, Chem. - A Eur. J. 16 (2010) 6326–6337, https://doi.org/
10.1002/chem.201000155.
[45] S.P. Gupta, M. Gupta, S.K. Pal, Highly resolved morphology of room-
temperature columnar liquid crystals derived from triphenylene and
multialkynylbenzene using reconstructed electron density maps,
ChemistrySelect 2 (2017) 6070–6077, https://doi.org/10.1002/slct.201701117.
[46] N. Godbert, T. Pugliese, I. Aiello, A. Bellusci, A. Crispini, M. Ghedini, Efficient,
ultrafast, microwave-assisted syntheses of cycloplatinated complexes, Eur. J.
Inorg. Chem. (2007) 5105–5111, https://doi.org/10.1002/ejic.200700639.
[47] D.L. Davies, M.P. Lowe, K.S. Ryder, K. Singh, S. Singh, Tuning emission
wavelength and redox properties through position of the substituent in
iridium(iii) cyclometallated complexes, Dalt. Trans. 40 (2011) 1028–1030,
https://doi.org/10.1039/c0dt01311k.
columnar liquid crystals, J. Appl. Crystallogr. 47 (2014) 668–679, https://doi.
org/10.1107/S1600576714003240.
[68] R. Kruszynski, T. Sieran´ ski, Can stacking interactions exist beyond the
commonly accepted limits?, Cryst. Growth Des. 16 (2016) 587–595, https://
doi.org/10.1021/acs.cgd.5b00852.
´
´
[69] K. Molcanov, B. Kojic-Prodic, Towards understanding
p-stacking interactions
between non-Aromatic rings, IUCrJ 6 (2019) 156–166, https://doi.org/10.1107/
S2052252519000186.
[70] A. Ionescu, R. Caligiuri, N. Godbert, A. Candreva, M. La Deda, E. Furia, M.
Ghedini, I. Aiello, Electropolymerizable IrIII complexes with b-ketoiminate
ancillary ligands, Chem.
10.1002/asia.201900521.
- Asian J. 14 (2019) 3025–3034, https://doi.org/
[71] I. González, D. Cortés-Arriagada, P. Dreyse, L. Sanhueza-Vega, I. Ledoux-Rak, D.
Andrade, I. Brito, A. Toro-Labbé, M. Soto-Arriaza, S. Caramori, B. Loeb, A Family
of IrIII complexes with high nonlinear optical response and their potential use
in light-emitting devices, Eur. J. Inorg. Chem. 2015 (2015) 4946–4955, https://
doi.org/10.1002/ejic.201500505.
[72] K.A. O’Donoghue, J.M. Kelly, P.E. Kruger, Unusual photophysical switching in a
Ru(ii) diimine DNA probe caused by amide functionalisation, J. Chem. Soc.
Dalt. Trans. 4 (2004) 13–15, https://doi.org/10.1039/b312524f.
[73] K.Y. Zhang, S.P.Y. Li, N. Zhu, L.W.S. Or, M.S.H. Cheung, Y.W. Lam, K.K.W. Lo,
Structure, photophysical and electrochemical properties, biomolecular
interactions, and intracellular uptake of luminescent cyclometalated iridium
(III) dipyridoquinoxaline complexes, Inorg. Chem. 49 (2010) 2530–2540,
https://doi.org/10.1021/ic902465b.
[48] K. Hideo, S. Yoshiyuki, Selective one-pot synthesis of facial tris-ortho-
metalated Iridium (III) complexes using microwave irradiation, Chem. Lett.
32 (2003) 252–253.
12

F. Scarpelli, L. Ricciardi, M. La Deda et al.
Journal of Molecular Liquids 334 (2021) 116187
[74] S. Serroni, S. Campagna, A. Juris, M. Venturi, V. Balzani, G. Denti, Tetranuclear
bimetallic complexes of ruthenium, osmium, rhodium, and iridium. synthesis,
absorption spectra, luminescence, and electrochemical properties, J. Am.
Chem. Soc. 116 (1994) 9086–9091, https://doi.org/10.1021/ja00099a026.
[75] L. Ricciardi, M. La Deda, A. Ionescu, N. Godbert, I. Aiello, M. Ghedini, M. Fusé, I.
Rimoldi, E. Cesarotti, Luminescent chiral ionic Ir(III) complexes: Synthesis and
photophysical properties, J. Luminescence 170 (2016) 812–819, https://doi.
org/10.1016/j.jlumin.2015.08.003.
[77] R.D. Costa, E. Ortí, H.J. Bolink, F. Monti, G. Accorsi, N. Armaroli, Luminescent
ionic transition-metal complexes for light-emitting electrochemical cells,
Angew. Chemie
anie.201201471.
- Int. Ed. 51 (2012) 8178–8211, https://doi.org/10.1002/
[78] R.D. Gillard, R.E.E. Hill, R. Maskill, Optically active co-ordination compounds.
Part XX. Reactions of 1,10-phenanthroline co-ordinated to Cobalt(III), J. Chem.
Soc. (1970) 1447–1451, https://doi.org/10.1039/J19700001447.
[79] C. Zhou, Q. Wang, Properties of a copper (I) complex, (2010) 605–611, doi:
10.1007/s11243-010-9370-1.
[76] Hexaazatriphenylene P Didier, I. Ortmans, A. Kirsch-De Mesmaeker, R.J. Watts,
Electrochemistry and absorption and emission spectroscopy of new ortho-
metalated complexes of Rh(m) and Ir(m) with the, 1993.
13